NOTE: As their name suggests hints are not exactly Battlefield 3 cheats, and are usually just simple (but very useful) tips on how you can unlock secret level, features, find hidden areas and such. Hopefully these will make playing Battlefield 3 even more entertaining.

Trophies
1st Loser (Silver): 2nd MVP in a ranked match
Army of Darkness (Bronze): Shot out the 4 lights with 4 bullets in Night Shift
Army of Two (Gold): Completed all co-op missions on Hard
Between a rock and a hard place (Bronze): Beat Solomon, flawlessly, in The Great Destroyer
Bullseye (Bronze): Saved the hostages without alerting any enemies in Drop 'em Like Liquid
Butterfly (Bronze): Took down the jet in one attempt in Rock And A Hard Place
Car Lover (Bronze): Completed the mission without losing a humvee in Operation Exodus
Colonel (Gold): Rank 45 achieved!
Decorated (Gold): Received one of each ribbon in the game
In the nick of time (Bronze): Disarmed the bomb in under 20 seconds in The Eleventh Hour
Infantry Efficiency (Bronze): Received all 4 weapon efficiency ribbons
Involuntary Euthanasia (Bronze): Killed the 2 soldiers before the building fell on them in Uprising
It's better than nothing! (Silver): 3rd MVP in a ranked match
Lock 'n' Load (Silver): Unlocked all unique co-op weapons
M.I.A (Bronze): Took your first enemy Dog Tag
Most Valuable Player (Silver): MVP in a ranked match
Ninjas (Bronze): Reached the VIP without setting off the alarm in Exfiltration
Not on my watch (Bronze): Protected Chaffin from the soldiers in the street in Operation SwordbreakerOoh-rah! (Silver): Completed the campaign story
Platinum Trophy (Platinum): Collect all other Battlefield 3 Trophies
Practice makes perfect (Bronze): each of the targets in the gun range in Kaffarov
Push On (Bronze): Reached the garage without going into man-down state in Hit and Run
Roadkill (Bronze): Kicked the car and killed the soldiers in Uprising
Scrap Metal (Bronze): Destroyed 6 enemy tanks before reaching the fort in Thunder Run
Semper Fidelis (Gold): Completed the campaign story on Hard
Support Efficiency (Bronze): Received all 4 support efficiency ribbons
The Professional (Bronze): Completed the street chase in Comrades in under 2 minutes 30 seconds without dying
Two-rah! (Silver): Completed all co-op missions
Twofor (Bronze): Took down 2 enemies with 1 bullet in Night Shift
Untouchable (Bronze): Completed the mission without using the fire extinguisher in Fire From The Sky
Vehicle Warfare (Bronze): Received all 3 vehicle warfare ribbons
What the hell *are* you? (Bronze): Took a Russian Dog Tag in the forest ambush in Rock And A Hard Place
You can be my wingman anytime (Bronze): Completed Going Hunting in a perfect run

Back to Karkand Trophies
The 'Back to Karkand' DLC patch added the following five trophies to the Battlefield 3 trophy set:

Complete Warrior (Silver): Got a kill with the following weapons in a single life: Assault Rifle, Jet, Tank
Gunslinger (Bronze): Got 10 kills with each of the ten Back to Karkand weapons
Jaws (Bronze): Took a swim in the Oman Hotel swimming pool
Like a Boss (Silver): Got a kill with the skid loader
Third Tour (Bronze): Got a kill with each of the following vehicles: BTR-90, DPV and F-35

Bite your finger (Silver): Found the secret reptile
Extreme Hoarder (Bronze): Picked up 50 weapons in Scavenger mode
Handyman (Bronze): Unlocked all xbow parts
Home made javelin (Bronze): Destroyed an enemy vehicle using the xbow
Pocket full of death (Silver): Without dying, got a kill with xbow, primary weapon, and hand grenade

Close Quarters Trophies
Complete Warrior (Silver): Got a kill with the following weapons in a single life: Assault Rifle, Jet, Tank
Deadly tools (Silver): Without dying, get a kill with a Carbine, Pistol and Rocket Launcher
Dominator (Bronze): Won a round of Conquest Domination
Grinding the Crack (Bronze): Fell over the edge on Ziba Tower
Gunslinger (Bronze): Got 10 kills with each of the ten Back to Karkand weapons
Jaws (Bronze): Took a swim in the Oman Hotel swimming pool
Like a Boss (Silver): Got a kill with the skid loader
Men of Calibre (Bronze): Completed a round of Gun Master
Show of Force (Silver): Got 10 kills with all ten CQ weapons
Third Tour (Bronze): Got a kill with each of the following vehicles: the BTR-90, DPV and F-35.

Battlefield 3: End Game Trophies
There are 3 Bronze Trophies and 2 Silver Trophies.: Type
AA's Revenge (Bronze): Destroy an air vehicle using the AA jeeps
Capture the Flag (Bronze): Capture 1 flag while playing Capture the Flag
Heavy Lifter (Bronze): Kill an enemy after successfully paradropping an IFV
It's No Sidecar (Silver): Get a kill from the passenger position on a motorcycle
Transport Pilot (Silver): Transport a flag carrier in an air vehicle while playing Capture the Flag